Searching for overlooked TDEs in the 4XMM catalogue

Abstract

Tidal disruption events (TDEs) are usually discovered as bright transients, either in the X-ray or optical/UV band. These events are often characterized by a "super-soft" emission in the X-ray band, which has not been observed in any other extragalactic source, with few exceptions (novae and supersoft active galactic nuclei, AGN), which can however be distinguished by their optical behavior. By cross-correlating optical and X-ray catalogs and filtering for extremely steep (photon index Γ > 3) and highly luminous (L X > 10 41 erg s −1 ) objects in external galaxies nuclear regions, we aim to detect overlooked TDEs. With our blind search, we retrieved about 60 sources. Among these, 36 sources show steeper-than-usual spectra, but, with their optical classification, can be considered standard AGNs. Instead, fifteen are well-studied supersoft AGNs or TDEs, demonstrating the efficiency of our selection. The remaining 9, are previously unknown sources. Five are extremely soft-excess dominated AGNs, while 4 sources are optima TDE candidates. In this work, we focus on these 4 latter sources.